The use of carbon dioxide for the pre-slaughter stunning of poultry was first proposed in the mid-1950's, Drewniak, et al., 1955, U.S.D.A. Circular 1958. The first commercial-scale, in-line gas stunner was designed a few years later, Kotula, et al., 1961, Poultry Sci., 40:213. However, technological limitations of the time combined with the development of cheaper electrical stunners that met the existing needs of processors, prevented further use of gas stunning by the poultry industry.
The electrical stunning procedure involves removing birds from a transport crate, individually shackling them by their legs, conveying each shackled bird to an electric stunning bath in which the head of the bird is immersed in water, which acts as a live electrode, and current passes through the bird to ground via the shackle. The electric stunning process causes electroplectic convulsions which result in hemorrhaging in the muscles of the breast and legs and broken bones in the carcasses, particularly in the collar regions. These conditions lead to downgrading of poultry carcasses.
More recently, U.S. Pat. No. 5,152,714 to Audsley, et al. describes a method for treatment of poultry by exposure to an atmosphere depleted in oxygen for a sufficient period of time to cause the poultry to undergo what is described as anoxic convulsions. In actuality, the convulsions are clonic convulsions which are induced by anoxia, i.e., deprivation of oxygen. As stated in the Audsley, et al. patent, "it is very much preferred to effect slaughter by subjecting them [the poultry] to the atmosphere for a sufficiently long period of time for the poultry to die". The conditions described in the Audsley, et al. patent would indeed result in death of the poultry of the size being treated in the Audsley, et al. patent under the time and inert gas concentrations utilized.
In accordance with the present invention, it has been determined that it is highly beneficial to avoid clonic convulsions prior to slaughter of poultry. In accordance with the present invention, the poultry are subjected to conditions sufficient to effect relaxation of the poultry and further conditions sufficient to render the poultry unconscious prior to slaughter.